1. Field of the Invention
The present invention relates to sintered shapes of silicon carbide and manufacture of the same, more particularly relates to sintered shapes of silicon carbide including oxides of rare earth elements and manufacture of the same.
2. Discussion of the Prior Art
Silicon carbide has been widely used of its excellent hot strength, thermal shock resistance, acid resistance, abrasion resistance and a high creep limit as high temperature resistant shapes and high temperature heating element, and recently its applications have been rapidly enlarged in the fields of high temperature structural material and anti-abrasive material.
However, due to the sintering difficulty of silicon carbide (hereinafter referred to as SiC), it is generally difficult to obtain dense and sintered shapes of high strength. Therefore, there have been used to manufacture such sintered shapes the hot pressing procedure with admixture of Al.sub.2 O.sub.3, iron oxides, AlN, BeO, Be, B, B.sub.4 C, BN, Al, AlPO.sub.4 as sintering assist, and the reaction sintering procedure wherein a mixture of SiC and C powder is reacted with molten or gaseous silicon. These procedures can not provide complicated configuration of the shapes and are not suitable to mass production. The presently most suitable process for manufacture of sintered SiC shapes is the non-pressure sintering procedure which involves mixing SiC powder with C and B as sintering assists and shaping into a green compact and sintering under free of pressure, as disclosed in the U.S. application Ser. No. 409,073. In the sintered shape of SiC produced by the above procedure, boron carbide resulting from the reaction of B and C promotes the sintering of SiC powder. It has been discovered that oxide sintering assists used in the hot pressing procedure has no effect on the sintering promotion in the non-pressure sintering procedure, and generally such oxides are deemed to be noxious in the non-pressure sintering of silicon carbide.